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Depression is the leading cause
of disability in the world.

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In the United States,

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close to 10% of adults 
struggle with depression.

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But because it's a mental illness,

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it can be a lot harder to understand,
than say, high cholesterol.

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One major source of confusion is
the difference between having depression

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and just feeling depressed.

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Almost everyone feels down
from time to time.

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Getting a bad grade,

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losing a job,

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having an argument,

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even a rainy day can bring on
feelings of sadness.

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Sometimes there's no trigger at all.

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It just pops up out of the blue.

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Then circumstances change,

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and those sad feelings disappear.

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Clinical depression is different.

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It's a medical disorder,

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and it won't go away 
just because you want it to.

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It lingers for at least 
two consecutive weeks,

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and significantly interferes 
with one's ability to work,

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play,

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or love.

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Depression can have a lot
of different symptoms:

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a low mood,

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loss of interest in things
you'd normally enjoy,

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changes in appetite,

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feeling worthless or excessively guilty,

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sleeping either too much or too little,

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poor concentration,

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restlessness or slowness,

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loss of energy,

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or recurrent thoughts of suicide.

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If you have at least five
of those symptoms,

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according to psychiatric guidelines,

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you qualify for a diagnosis of depression.

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And it's not just behavioral symptoms.

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Depression has physical manifestations
inside the brain.

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First of all,

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there are changes that could be seen
with the naked eye

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and x-ray vision.

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These include smaller frontal lobes
ad hippocampal volumes.

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On a more microscale,

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depression is associated 
with a few things:

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the abnormal transmission or depletion
of certain neurotransmitters,

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especially serotonin, norepinephrine,
and dopamine,

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blunted circadian rhythms,

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or specific changes in the REM
and slow-wave parts of your sleep cycle,

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and hormone abnormalities,

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such as high cortisol and deregulation
of thyroid hormones.

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But neuroscientists still don't have
a complete picture

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of what causes depression.

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It seems to have to do with a complex
interaction between genes and environment,

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but we don't have a diagnostic tool

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that can accurately predict where
or when it will show up.

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And because depression symptoms
are intangible,

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it's hard to know who might look fine
but is actually struggling.

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According to the National Institute
of Mental Health,

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it takes the average person
suffering with a mental illness

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over ten years to ask for help.

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But there are very effective treatments.

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Medications and therapy compliment
each other to boost brain chemicals.

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In extreme cases,
electroconvulsive therapy,

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which is like a controlled seizure
in the patient's brain,

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is also very helpful.

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Other promising treatments,

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like transcranial magnetic stimulation,

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are being investigated, too.

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So, if you know someone 
struggling with depression,

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encourage them gently to seek out
some of these options.

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You might even offer to help
with specific tasks,

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like looking up therapists in the area,

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or making a list of questions
to ask a doctor.

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To someone with depression,

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these first steps can seem insurmountable.

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If they feel guilty or ashamed,

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point out that depression 
is a medical condition,

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just like asthma or diabetes.

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It's not a weakness 
or a personality trait,

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and they shouldn't expect themselves
to just get over it

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anymore than they could will themselves
to get over a broken arm.

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If you haven't experienced 
depression yourself,

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avoid comparing it to times
you've felt down.

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Comparing what they're experiencing
to normal, temporary feelings of sadness

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can make them feel guilty for struggling.

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Even just talking about 
depression openly can help.

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For example, research shows that asking
someone about suicidal thoughts

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actually reduces their suicide risk.

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Open conversations about mental illness
help erode stigma

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and make it easier 
for people to ask for help.

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And the more patients seek treatment,

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the more scientists will learn
about depression,

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and the better the treatments will get.